After years of development, the light emitting diode has been widely applied in different fields like display, indication, back light and lighting. III-V group compound is the mainstream semi-conductor material for fabricating light emitting diode, in which, GaN-based material and AlGaInP-based material are most popular. Since the conventional P-type III-V group semiconductor material has poor current spreading performance, to enable even injection of current into the light-emitting layer, a transparent conducting layer is added over the p-type material layer. Among many materials as transparent conducting layer to improve current spreading effects like ITO, CTO, InO and ZnO, the ITO (Indium Tin Oxide) is most widely applied. The ITO film refers to indium tin oxide semiconductor transparent conducting film, and the ITO meets two index requirements, namely low resistivity and high light transmittance. In comparison to other transparent semiconductor conducting films, ITO has good chemical stability and heat stability.
Today, evaporation-deposited ITO tends to be replaced by sputtered ITO which has excellent performance and such advantages as voltage reduction and luminance improvement. However, the sputtered ITO has smooth surface that leads to a poor adhesiveness to the metal electrode. In particular, when above 250° C., thermal expansivity difference between the ITO and the metal electrode material gets larger, making stress between films increase accordingly, thus greatly reducing electrode adhesiveness.
In industry, main methods to solve such electrode dropping include roughening ITO film or adjusting film process parameters. These technologies, however, are still not perfect and have their own deflects. For example, the sputtered ITO microstructure generally comprises 30 nm-100 nm grains while wet roughening with solution is isotropic for each grain etching, therefore, the roughed surface remains flat. And adjustment of film process parameters, like sectional coating or reduction of rate in general, is difficult for it has to consider photoelectric parameter and electrode adhesiveness at the same time.